The present invention relates to a method for forming magnetic poles in thin film magnetic heads by a frame plating technique.
In recent years, magnetic recording has been performed at much higher densities. With this, thin film magnetic heads using soft magnetic thin films for magnetic poles, and magnetoresistance (MR) heads making use of magnetoresistance effect for reproducing purposes have been under remarkable developments. An MR head is designed to read external magnetic signals through a resistance change in a reading sensor formed of magnetic material. A characteristic feature of the MR head is that high outputs are achievable even when magnetic recording is performed at high linear densities because outputs are not dependent on its relative speed with respect to a recording medium. For the MR head that is a reproducing head, an MR induction composite head is used, in which an MR head portion is provided in the form of an integral piece of an induction head portion for recording purposes.
A thin film magnetic head is typically fabricated by stacking on an insulating substrate a lower magnetic pole, a gap layer, a coil surrounded by an insulating film, an upper pole and a protective film in the described order. Magnetic pole formation is usually achieved by a so-called frame plating technique. For instance, the frame plating technique is described in JP-B 56-36706. The frame plating technique is used to form members having limited dimensional tolerances such as magnetic poles in thin film magnetic heads. According to the frame plating technique, the article to be plated is first provided with a plating frame. To form magnetic poles, the plating frame is formed by the patterning of a resist film in such a manner that a space (hole) commensurate with magnetic pole shape is left.
In recently developed magnetic heads, the widths of the tip portions of magnet poles are very narrow as typically expressed by 2 .mu.m or lower to be compatible with recording track width decreases incidental to recording density increases, and so much severer conditions are imposed on the dimensional accuracy demanded. On the other hand, the thickness of an upper magnetic pole (the length of the magnetic pole), for instance, should be 3 .mu.m or lower. A plating film formed in the form of an upper magnetic pole during the fabrication of a thin film magnetic head decreases in thickness under the influences of etching or other operations in the subsequent steps. A plating frame for forming the tip portions of magnetic poles should also be thicker than required because the resist film used is poor in the capability of tracing thickness (hereinafter called the thickness traceability), as will be described later. For these reasons, the plating film must have a thickness of at least 4 .mu.m so as to form an upper magnetic pole of at least 3 .mu.m in thickness. Correspondingly, it is required for the plating frame to have a height of at least 4 .mu.m. When magnetic poles for such narrow tracks are formed, therefore, it is required to form in a resist film a narrow yet relatively deep space with a depth to width ratio of at least 2.
A general positive resist has so far been used for plating frame material. It is understood that the term "general positive resist" used herein refers to a mixture of an alkali-soluble phenol resin and a sensitizer (e.g., naphthoquinonediazide). When used to form magnetic poles in a thin film magnetic head, the positive resist for the plating frame should have three major properties:
1) it should have high resolution; PA1 2) upon coated on a step, it should provide a film unlikely to vary in thickness between on the step and the vicinity of a gap adjacent to a lower portion of the step (or it should be excellent in the thickness traceability); and PA1 3) it is well resistant to plating (chemicals, compression, and heat). A conventional positive resist is unsuitable for the formation of magnetic poles for narrow tracks which are required to have high dimensional accuracy, as explained below. This is because the conventional positive resist is found to be insufficient in terms of properties 1) and 2). PA1 (1) A method for fabricating a magnetic pole in a thin film magnetic head by a frame plating technique, wherein: PA1 (2) The fabrication method of the above (1), wherein said space has a sectional depth of up to 10 .mu.m.
When magnetic poles for narrow tracks are formed, it is required to form a plating frame having a narrow yet relatively deep space, as mentioned above. When a conventional positive resist is used to form a narrow yet relatively deep space in a resist film, however, a bottom portion of the space has a shape defected called tailling, as can be seen from FIG. 5, due to insufficient resolution. Such disorders in the sectional shape of the space make the width of the space inconsistent in the depth-wise direction.
Poor thickness traceability poses such problems as mentioned below. As depicted in FIG. 2 A, an upper magnetic pole in a thin film magnetic head is formed on an insulating film 23 including a coil 24 therein with an electroconductive seed film 3 located between them. In the vicinity of the coil 24, there is a step of about 10 .mu.m in height with respect to the vicinity of a gap (a left-handed portion of an insulating film 22 shown). For this reason, a plating frame for forming the upper magnetic pole is formed astride the step. A resist film 41 that provides the plating frame is usually formed by spin coating. When the resist is poor in the thickness traceability, however, it cannot faithfully trace the step. This in turn causes the resist film 41 to become too thick in the vicinity of the gap adjacent to a lower portion of the step, as depicted in FIG. 2 B. When the resist film becomes too thick, it is difficult to form a space of good dimensional accuracy upon patterning. A portion of the plating frame in the vicinity of the gap adjacent to the lower portion of the step is provided to form the tip of the magnetic pole. When the dimensional accuracy of a space in that frame portion is worse, a problem arises upon the formation of a magnetic pole for narrow tracks. This may be avoided under forming conditions preset in such a manner that the thickness of the resist film is optimized in the vicinity of the gap adjacent to the lower portion of the step. In this case, the thickness of the resist film 41 on the step becomes too thin, as depicted in FIG. 2 C, resulting in a (overhanging) phenomenon in which a yoke portion of the magnetic pole formed on the step goes over the plating frame. In this case, the volume of the yoke portion of the magnetic pole becomes variable because it is substantially impossible to place the amount of overhanging under control. For this reason, it is difficult to fabricate magnetic heads having consistent properties.
It is therefore an object of the present invention to make it possible to form a plating frame having a narrow yet relatively deep space of good dimensional accuracy when a magnetic pole in a thin film magnetic head is formed by a frame plating technique.